PIERCE COUNTY, Wash. -- Hundreds are now behind bars, accused of selling children for sex.

Over the weekend, federal agents worked with the Pierce County Sheriff's Office and local police officers to look for children caught in the world of prostitution. Authorities say child sex rings are thriving in the Northwest, thanks to the Internet.

"People who aren't willing to go drive around and pick someone up, and unfortunately a lot more women are partaking in prostitution due to the fact that they don't have to go walk the streets now," said Pierce County Det. Ed Troyer.

Over the weekend, investigators in Tacoma, Lakewood and Pierce County worked with the FBI to make 19 arrests, which included three pimps, one child prostitute and 15 young women, mostly 18 and 19 years old.

Across the country, the FBI arrested 642 people. More importantly, they rescued 47 children, some as young as 13, who were reportedly being sold for sex.

"It is very concerning," said Lt. Heidi Hoffman of Lakewood police. "A lot of times these girls get wooed in by money or trips, but what they end up getting is beat up, abused and left, addicted on drugs."

Local authorities say they'll continue working with the FBI to catch more people selling children for sex and to rescue more children caught in a cycle that can destroy their lives.

"If we don't get to them now and disrupt them while they're juveniles, you are going to lose them forever," said Troyer.

The FBI is now working with authorities in both Snohomish and King Counties to increase their local focus, and they hope to have a full Pacific Northwest Task Force in place soon.